Exhaust heat exchanger in particular for motor vehicles

ABSTRACT

The invention relates to an exhaust heat exchanger ( 1 ), in particular an exhaust cooler for motor vehicles with exhaust recycling, comprising a housing sleeve ( 2 ) for a coolant and a nest of tubes ( 3 ) with exhaust flowing through and coolant circulating around the above which are mounted on the housing sleeve by means of tube plates ( 4 ), whereby said nest of tubes, the tube plate and the housing sleeve form a closed force flow. According to the invention, a sliding seating ( 5 ) is arranged in the force flow, either in the housing sleeve or between a tube plate and the housing sleeve. The various expansions of the nest of tubes and of the housing sleeve are thus compensated for, such that unsupportable high loads do not occur in the components of the exhaust heat exchanger.

The invention relates to an exhaust heat exchanger in particular formotor vehicles having an exhaust gas recirculation system (AGR),composed of a housing jacket for a coolant, and of a nest of pipesthrough which exhaust gas flows on the inside and around which coolantflows on the outside and which is held in the housing jacket by means ofpipe plates, the nest of pipes, pipe plates and housing jacket formingan enclosed force flux—such an exhaust heat exchanger has been disclosedby DE-A 199 07 163 by the applicant.

This known exhaust heat exchanger is an exhaust gas radiator such as isused in motor vehicles for recirculating exhaust gases in order to coolthe hot exhaust gases. The exhaust gas radiator which is manufacturedfrom stainless steel is essentially composed of a housing with a housingjacket through which a coolant flows, said coolant being removed fromthe coolant circuit of the internal combustion engine of the motorvehicle. A nest of pipes whose pipe ends are held by pipe plates whichare themselves connected to the housing jacket is arranged in thehousing jacket. The pipe ends are welded tightly to the pipe plates andthe pipe plates are welded at the circumference to the housing jacket.In this respect the two pipe plates form, together with the housingjacket, what are referred to as fixed bearings. When this exhaust gasradiator operates, the pipes and housing jacket heat up to differingdegrees because the exhaust gases flowing through the pipes have ahigher temperature than the coolant flowing around the housing jacket.As a result, different degrees of expansion between the nest of pipesand the housing jacket occur, which leads to thermally induced stresses,i.e. compressive stresses in the pipes and tensile stresses in thehousing jacket and flexural stresses in the pipe plates. The pipes ofthe nest of pipes which form the pipe plates, which hold the pipe ends,and the housing jacket thus form an enclosed force flux in which thepipes are supported on the housing jacket by means of the pipe plates.In particular in the case of exhaust gas radiators with a long length,such as are used in utility vehicles, the stresses which occur owing tothe different degrees of expansion can lead to individual componentsfailing or to the connection between the pipe plates being destroyed.

The object of the present invention is to reduce these thermally inducedstresses, i.e. to decrease the resulting stresses in the components ofthe exhaust heat exchanger in order to achieve higher safety and alonger service life for the exhaust heat exchanger mentioned in thebeginning.

The means of solving this object is proposed according to claim 1 inthat a sliding fit is arranged within each force flux, i.e. a fitbetween two components which can slide in relation to one another, thatis to say what is referred to as a loose bearing, in contrast to a fixedbearing such as is present in the prior art of the generic type. Such asliding fit compensates for the different degrees of expansion of thenest of pipes and housing, i.e. the abovementioned stresses do not occurat all. The sliding fit can be installed structurally at any desiredlocation of the force flux, it being necessary where possible to avoidthe coolant and exhaust gas becoming mixed with one another, which couldlead to damage to the engine.

According to one advantageous development of the invention, the slidingfit is arranged in the housing. This solution has the advantage thatrelatively large sliding surfaces are available and that there is norisk of coolant becoming mixed with the exhaust gas, or vice versa whenthere is a leakage due to the sliding fit. The housing jacket is dividedtransversely with respect to the direction of the force flux, and bothhousing parts are assembled in a telescopic fashion so that when thenest of pipes experiences severe expansion they can be pulled apart fromone another without stresses occurring in the housing jacket, in thepipe plate or in the nest of pipes.

According to one advantageous development the sliding fit is composed ofan outer ring and an inner ring between which a plastic sliding layer isarranged in order to improve the sliding properties. Both rings arepushed onto the end regions of the housing parts of the prefabricatedsliding fit, and preferably bonded to said housing parts. The bondingavoids excessive application of heat and thus possible distortion of thecomponents. The fitting on and bonding of the internal ring and outerring is advantageous in particular when the housing jacket has asomewhat rugged contour: the surfaces of the inner and outer ring whichslide one on the other can be configured as simple contours which can besealed satisfactorily, for example, as a polygonal contour.

According to one advantageous development of the invention, the slidingfit is arranged between one of the two pipe plates and the housing. Thissolution thus provides a fixed bearing and a loose bearing for the nestof pipes. As a result, the nest of pipes can expand freely with respectto the housing jacket so that the abovementioned compressive stresses donot occur in the pipes and the abovementioned tensile stresses do notoccur in the housing jacket. The pipe plate which is embodied as asliding fit thus has a sliding surface which slides along an assignedsliding surface of the housing jacket and is sealed with respectthereto, preferably by means of O rings.

According to one development of the invention, a drainage, which isconnected to the atmosphere, is provided between the O rings, i.e.between two O rings. This drainage provides the advantage that thecoolant and exhaust gas cannot mix if an O ring or a corresponding sealfails because either the exhaust gas or the coolant escape to theoutside through the drainage.

According to one advantageous development, the drainage is embodied as aslit in the housing, i.e. the housing is divided by a joint and is heldspaced apart by means of spacer sleeves which are arranged on thecircumference. If the seal fails, exhaust gas or coolant can beconducted away to the outside through the slit.

According to one advantageous alternative, the drainage is formedbetween two O rings as an annular groove in which the leakage fluid orthe leakage gas collect and can escape to the outside via drainageopenings which are arranged in the annular groove. This solution isstructurally simple since the housing does not need to be divided.

Exemplary embodiments of the invention are illustrated in the drawingand will be described in more detail below. In said drawing:

FIG. 1: shows a perspective view of an exhaust gas radiator with asliding fit in the housing jacket,

FIG. 2 shows the exhaust gas radiator according to FIG. 1 in alongitudinal section,

FIG. 2 a shows a side view of the exhaust gas radiator according to FIG.2,

FIG. 2 b shows a section through the exhaust gas radiator according toFIG. 2 in the sectional plane IIb-IIb,

FIG. 2 c shows the sliding fit as an individual unit,

FIG. 3 shows a further embodiment of an exhaust gas radiator with thesliding fit between the pipe plate and housing jacket,

FIG. 4 shows a section through the exhaust gas radiator according toFIG. 3 in the plane IV-IV,

FIG. 5 shows a modification of the exhaust gas radiator according toFIG. 3 with the drainage groove, and

FIG. 6 shows a schematic view of the stresses in an exhaust gas radiatoraccording to the prior art.

Firstly, FIG. 6 shows the stress conditions in an exhaust gas radiatoraccording to the prior art which is cooled by coolant. This schematicillustration corresponds to an exhaust gas radiator according to theprior art by the applicant which is mentioned at the beginning. Such aknown heat exchanger 60 is composed of a housing jacket 61 which holds anest of pipes which is composed of pipes 62 and whose ends are held inpipe plates 63, 64. The pipes 62 are connected at both ends to the pipeplates 63, 64 in a secure and sealed fashion, for example, by means ofwelded connections. The pipe plates 63, 64 are securely connected to thehousing jacket 61 at the circumference by means of welded connections65, 66. In this way, both pipe plates 63, 64 form two fixed bearingswith the housing jacket 61. When such an exhaust gas radiator 60 isoperating, the hot exhaust gas flows through the pipes 62, while coolantat a considerably lower temperature is applied to the inside of thehousing jacket 61. As a result, different degrees of expansion betweenthe pipes 62 and the housing jacket 61 are produced. For this reason,compressive stresses, which are characterized by arrows and the letter C(compression) which are directed one against the other are formed in thepipes 62. These compressive stresses continue further to the housingjacket 61 via the pipe plates 63, 64 and the welded connections 65, 66,tensile stress, characterized by the letter T (tension) and arrowspointing away from one another, then building up in the said housingjacket 61. The tensile stresses T and the compressive stresses C thusform an enclosed force flux or force flux ring over the pipe plates 63,64 in which flexural and shearing stresses (not illustrated) occur.

FIG. 1 shows a perspective view of an exhaust gas radiator 1 for a motorvehicle with an exhaust gas recirculation system (AGR). Such exhaust gasrecirculation systems are used for recirculation cooling of the hotgases of an internal combustion engine (not illustrated) before they arecombined with the intake air and fed to the intake tract of the internalcombustion engine. The exhaust gas radiator 1 is composed of a housingjacket 2 which holds in it a nest of pipes which are composed of exhaustgas pipes 3. The ends of the pipes 3 are fastened to a pipe plate 4which is itself welded to the housing jacket 2. The housing jacket 2 hasa sliding fit 5 which is composed of an outer ring 6 and an inner ring7.

FIG. 2 shows the exhaust gas radiator 1 according to FIG. 1 in asectional view, i.e. in a longitudinal section through the exhaust gaspipes 3 which are held at the ends in the two pipe plates 4 and 5, i.e.are, for example, connected to the pipe plates 4, 5 by means of a weldedconnection. Said pipe plates 4, 5 are connected at the circumference tothe housing jacket 2 in a secure and fluid-tight fashion by means ofwelded connections 6, 7. The exhaust gas of the internal combustionengine (not illustrated) flows through the exhaust gas pipes 3, andcoolant, which is removed from the coolant circuit (not illustrated) ofthe internal combustion engine, flows around the exhaust gas pipes 3,i.e. through the gaps 8 left between them. The connections for theinflow and outflow of the coolant for the housing jacket 2 are notillustrated for the sake of simplicity. The housing 2 is composed of twohousing parts 2 a and 2 b which have a joint 9. In the region of thisjoint 9, the housing part 2 b which is arranged to the right in thedrawing has a smaller cross section than the housing part 2 a which isillustrated to the left in the drawing. An outer ring 10 is attached tothe housing part 2 a, and an inner ring 11 is attached to the housingpart 2 b. The outer ring 10 and the inner ring 11 together form thesliding fit 5, which is illustrated as a detail in FIG. 2 c.

FIG. 2 c shows the end regions of the housing parts 2 a, 2 b in theregion of the joint 9, the end sides of the housing parts 2 a, 2 b beingspaced apart from one another by a gap s. The inner ring 11 is attachedto the housing part 2 b by bonding and the outer ring 10 is attached tothe housing part 2 a by means of a bonded connection. The outer ring 10overlaps the inner ring 11 and forms with it a sliding fit 13. A plasticlayer 14 is securely attached to the internal surface of the outer ring10 in the region of the sliding fit 13. In contrast, the outside of theinner ring 11 is metallically smooth, for example ground. This resultsin a low-friction sliding pairing between the plastic layer 14 and themetallic surface of the inner ring 11 for the sliding fit 13. Thesliding fit 13 is sealed with respect to the outside, i.e. with respectto the atmosphere, by means of two O rings 15 so that coolant cannotescape to the outside.

FIGS. 2 a, 2 b show the cross section of the exhaust gas radiator 1 as aview and as a section. It is apparent that the pipes 3 have arectangular cross section and are at approximately equal distances 16from one another. Owing to this arrangement of the pipes 3, anapproximately rectangular profile with shoulders 2 c is obtained for thecontour of the housing jacket 2 b. The contour of the inner ring 11 isadapted to this somewhat rugged contour which is bent by the shoulders 2c. In contrast, the outer contour 11 a of the inner ring is smoothed andhas an approximately polygonal profile without severe curvatures, andthis surface can therefore be manufactured relatively easily as a smoothsurface and can be sealed with respect to the inner surface of the outerring 10 using simple means such as O rings 15.

The outer ring 10 and inner ring 11, plastic sliding layer 14 and Orings 15 can be manufactured together as a prefabricated unit, i.e. as aprefabricated sliding fit 5, and then connected to the housing parts 2a, 2 b by means of the bonded connection already mentioned.

When the exhaust gas radiator 1 is operating, the sliding fit 5 ensuresthat the housing 2 and the housing parts 2 a and 2 b can follow therelatively severe expansion of the pipes 3 by moving in relation to oneanother—thermal stresses and the excessive stresses of the componentsare thus avoided.

FIG. 3 shows a further exemplary embodiment of the invention for asliding fit, i.e. an exhaust gas radiator 20 of which only the region ofthe sliding fit is represented as a detail. The exhaust gas radiator 20has a housing jacket 21 which comprises a coolant region 22 and anexhaust gas region 23. A pipe plate 24 in which exhaust gas pipes 25 areattached, for example by soldering or welding, is arranged inside thehousing jacket 21. The pipe plate 24 is adjoined by a hollow cylindricalregion which holds in each case one O ring 29, 30 in each of two annulargrooves 27, 28. The cylindrical attachment 26 has an outer slidingsurface 31 which bears in a sliding fashion against an inner surface 32of the housing jacket 21 and thus forms a sliding fit 31/32 with thehousing jacket 21. The housing 21 is divided by a slot 33 between thetwo O rings 29, 30. It thus has a left-hand housing part 21 a and aright-hand housing part 21 b. Both housing parts 21 a, 21 b are heldapart by a constant distance, i.e. the width of the slot 33, by means ofspacer sleeves (cf. FIG. 4) distributed over the circumference andattachment eyelets 35, 36 which are provided on the housing parts 21 a,21 b. The attachment of eyelets 35, 36 and the spacer sleeves 34 areclamped to one another by means of screw or bolt connections (notillustrated). The slot 33 is thus connected to the atmosphere, i.e. theoutside of the housing jacket 21.

FIG. 4 shows a section along the sectional plane IV-IV in FIG. 3, i.e.through the region of the slot 33 and the spacer sleeve 34. The crosssection of the pipes 25 is circular here.

When the exhaust gas radiator 20 is operating, hot exhaust gases flowthrough the region 23 into the interior of the pipes 25, around whichcoolant, which flows around the inside of the housing jacket 21 flows onthe outside, i.e. in the coolant region 22. Said housing jacket 21 istherefore at a lower temperature than that of the exhaust gas pipes 25.The greater degree of expansion of the exhaust gas pipes 25 iscompensated by the sliding fit 31/32, i.e. the pipes can expand freelywith respect to the housing jacket 21 by means of the pipe plate 24 andthe cylindrical attachment 26. The seal between the coolant region 22and exhaust gas region 23 is provided by means of the O rings 29, 30. Ifone of these O rings were to lose its sealing effect, coolant wouldleave the region 22 or exhaust gas would leave the region 23 and enterthe slot 33 and pass from there to the outside and into the atmosphere.This prevents either exhaust gas entering the coolant region 22 orcoolant entering the exhaust gas region 23 and thus causing damage.

FIG. 5 shows a modified exemplary embodiment of the exhaust gas radiator20 according to FIG. 3, i.e. an exhaust gas radiator 40 with acontinuous housing jacket 41 and a sliding fit 42 which corresponds tothe sliding fit 31/32 of the exemplary embodiment according to FIG. 3.An annular groove 45, which has a corresponding annular collar 46 (or anintegral bead), is integrally formed between two O rings 43, 44. Theannular groove 45 is connected to the atmosphere via a drainage opening47. The drainage which has been described above for the exemplaryembodiment according to FIG. 3, i.e. the conduction away of coolant orexhaust gas to the outside is thus possible in the same way. Anadvantage with this solution is that the housing 41 is in one piece andcan thus be manufactured more easily.

1. An exhaust heat exchanger, in particular for motor vehicles having anexhaust gas recirculation system (AGR), composed of a housing jacket fora coolant, and of a nest of pipes through which exhaust gas flows andaround which coolant flows and which is held in the housing by pipeplates, the nest of pipes, the pipe plates and the housing forming anenclosed force flux, characterized in that a sliding fit (5, 31, 3; 42)is arranged in the force flux.
 2. The exhaust heat exchanger as claimedin claim 1, characterized in that the sliding fit (5) is arranged in thehousing jacket (2).
 3. The exhaust heat exchanger as claimed in claim 1,characterized in that the sliding fit (31/32, 42) is arranged between apipe plate (24, 26) and the housing jacket (21, 21 a, 21 b).
 4. Theexhaust heat exchanger as claimed in claim 2, characterized in that thehousing jacket (2) is divided transversely with respect to the directionof the force flux and has an end region (2 a, 10) with a relativelylarge cross section and an end region (2 b, 11) with a relatively smallcross section, said regions overlapping in the direction of the forceflux and being guided and sealed so as to slide one in the other.
 5. Theexhaust heat exchanger as claimed in claim 4, characterized in that aplastic layer (14) is arranged as a sliding layer between the endregions (10, 11).
 6. The exhaust heat exchanger as claimed in claim 4,characterized in that sealing means (15) are arranged between the endregions (10, 11).
 7. The exhaust heat exchanger as claimed in claim 6,characterized in that the sealing means are embodied as O rings (15). 8.The exhaust heat exchanger as claimed in claim 4, characterized in thatthe end regions (2 a, 2 b) are formed by an outer ring (10) and an innerring (11) whose wall thickness is greater than that of the housingjacket (2).
 9. The exhaust heat exchanger as claimed in claim 5,characterized in that the plastic layer (14) is applied to the outerring (10) in a securely adhering fashion, and in that the inner ring(11) has a metallic smooth surface and forms a sliding fit (13) with theplastic layer (14).
 10. The exhaust heat exchanger as claimed in claim8, characterized in that the outer ring (10) and the inner ring (11) arebonded onto the housing part (2 a, 2 b).
 11. The exhaust heat exchangeras claimed in claim 8, characterized in that the outer ring (10), theinner ring (11), the plastic layer (14) and the O rings (15) areembodied as a prefabricated sliding fit (5) which is finally connectedto the end regions of the housing part (2 a, 2 b).
 12. The exhaust heatexchanger as claimed in claim 3, characterized in that the sliding fitis formed by a sliding surface (31) on the pipe plate and a slidingsurface (32) on the housing, which sliding surfaces (31, 32) are sealedby means of O rings (29, 30) between the coolant side (22) and exhaustside (23).
 13. The exhaust heat exchanger as claimed in claim 12,characterized in that a drainage (33; 45, 47) is arranged between two Orings (29, 30; 43, 44).
 14. The exhaust heat exchanger as claimed inclaim 13, characterized in that the drainage is embodied as acircumferential slit (33) which separates the housing (21) into twohousing parts (21 a, 21 b), and in that the housing parts (21 a, 21 b)are held spaced apart from one another by means of spacer sleeves (34).15. The exhaust heat exchanger as claimed in claim 14, characterized inthat the housing parts (21 a, 21 b) have attachment eyelets (35) whichare distributed over the circumference in the region of the slit (33)and between which the spacer sleeves (34) are arranged.
 16. The exhaustheat exchanger as claimed in claim 12, characterized in that thedrainage is embodied as an annular groove (45) in the housing (41),which annular groove (45) is connected to the atmosphere via at leastone drainage opening (47).